The present invention relates to a yarn, the use of the yarn to produce a preform, a preform comprising the yarn, a method for production of the preform, and its use in the production of a composite.
A known method of producing fiber-reinforced plastic components consists in first preparing a preform similar in form to the component, transferring the preform to a tool having the form of the component, and finally producing the desired component by addition of a matrix resin.
In contrast to preforms, prepregs (preimpregnated fibers) already contain both components (fibers and matrix resin) in the same ratio as in the final mixture, and are therefore resistant to bending, even in the form of the semi-finished product. To prevent premature unwanted reactions, this material must also be stored cool and even then has only a limited shelf life. On account of the material's flexural rigidity and its production in the form of large-width rolls, the use of prepregs is restricted to components of large surface area that are nearly planar. The presence of the matrix resin does not permit textile processing or wrinkle-free application of prepregs around narrow radii or on strongly contoured geometries, for example.
If flexible yarns are used for the production of preforms, it is possible to produce surfaces that are far more heavily curved. Moreover, the maximum shelf life of the preform is significantly improved as compared with prepregs, because the matrix resin is not added until the production of the composite material.
JP 2003 003376 A describes a carbon fiber bundle for production of a prepreg. The bundle comprises 20,000 to 100,000 filaments and is held together by a sizing agent containing polyoxyalkylene groups and epoxy groups. The carbon fiber bundle contains 0.5 to 3 wt.% of sizing agent relative to its total weight.
DE 27 46 640 A describes a carbon-fiber reinforced material on which a resin mixture containing an epoxy resin, a condensation product of an acid component and a hydroxyl component, and an oxyalkylene derivative of a phenol has been applied. The carbon fibers contain 0.01 to 10 wt.% of resin mixture relative to their total weight.
DE 39 42 858 A describes a sizing agent for carbon fibers that contains an epoxy resin and a nonionic emulsifier containing tertiary amino groups, at least one functional group capable of reacting with the epoxy resin, and at least one group with emulsifying action. 0.3 to 10 wt.% of sizing agent is said to be present on the fiber.
DE 20 33 626 A describes a method for production of a prepreg from mechanically high-grade fiber materials such as, in particular, fibers of glass, boron or carbon. The fibers are impregnated with a solution containing a curable polyadduct that contains free glycidyl groups and consists of triglycidyl isocyanurate, a curing agent and an organic solvent.
DE 201 20 447 U1 describes a preform consisting of a textile flat structure, such as a fabric or fiberwoven fabric layer, with a thermoplastic, non-crosslinked binder, which can be, for example, an epoxide, adhering to the surface of the textile flat structure. According to DE 201 20 447 U1, the binder is applied by, for example, spraying a binder solution on to the surface of the textile flat structure, whereby the binder solution contains powder particles that are uniformly dispersed in a solvent, and whereby the powder particles can consist exclusively of epoxy resin.
However, when a preform is produced from a textile flat structure, the binder coating is unevenly distributed over the thickness of the textile flat structure, and in some places, particularly where the yarns are in contact with one another, is almost absent. A preform of this type therefore often has low slip resistance, so that further handling of the preform is difficult or even impossible.
Additional disadvantages arise if the preform is to have perforations, which, if the preform is produced from textile flat structures, must in many cases be produced by cutting out material. This requires additional processing time, and the offcuts result in considerable loss of material and generate a corresponding amount of waste. This method for producing a preform is therefore cost- and labor-intensive, which is reflected in the costs of the composites produced from it.